In the traditional welding technical field, the temperature at the welding point increases rapidly in the welding process, and the post-welding temperature decreases rapidly as the welding point moves. Under the impact of temperature difference, a complex stress-strain state occurs in the weldment, high residual tension stress is produced at the weld seam, and the residual tension stress decreases as the distance from the weld seam increases. Owing to the existence of the complex and uneven stress-strain in the weldment, high warping deformation may be produced in the weldment after the weldment is cooled down. Welding clamps are indispensable auxiliary tools for welding of metal structures and an important constituent of the welding process. In the existing technology, usually reversed deformation method, skip-welding method, and weld seam hammering method, etc., are utilized to reduce the degree of post-welding deformation. Though these methods can reduce post-welding deformation to some degree, the post-welding deformation reduction effect is not ideal; the clamps and positioning devices used at present studying weld seam quality and post-welding performance of weldment are often very complex and costly, and cannot meet the requirement for adjusting positioning point and clamping force at will.
For example, Chinese Patent Application Document No. CN102601566A discloses a swing-type reversed deformation welding clamp for bridge board unit; however, the drawbacks of the welding clamp include: it requires multiple hydraulic cylinders for driving purpose, has complex composition, and involves high manufacturing cost.
For example, Chinese Patent Application Document No. CN103317279A discloses a multi-functional welding test clamp; however, the drawbacks of the clamp include: the weldment is at an suspending state, the clamp cannot be used to hold large-size plate parts, the clamping position of the weldment can't be selected at will, and high clamping force cannot be applied.
Therefore, it is of crucial importance to carry out research on the welding quality of a weldment clamped at different clamping positions and at different clamping levels, so as to find out optimal welding parameters and thereby improve the performance of the weldment.